Web Services and Transactions - OMG · Title: Web Services and Transactions Author: William Cox and...

Web Services and TransactionsObject Management Group

Web Services WorkshopFebruary 2003

William CoxSanjay Dalal

BEA Systems, Inc.http://www.bea.com

[email protected]@bea.com

http://www.bea.com/

mailto:[email protected]

mailto:[email protected]

2OMG Web Services Workshop February 2003Copyright 2003 BEA Systems, Inc All Rights Reserved

Agenda

• Web Services and Transactions– Long-running Transactions– Web Services

• Specifications and Standards• Compare

– WS-Transaction and WS-Coordination– Business Transaction Processing

• Driving Convergence• Conclusions• References


Why do Web Services Need Transactions?• Loosely-coupled• Distributed• Coordination is an issue except for single sequence

– Make error-prone complex transactions easier to program

• New requirements for independent participants– One coordinator can’t demand all participants follow the

coordinator’s business rules– Isolation hard to maintain—one transaction affects another

• XML-based transaction protocols for interoperability


The Case for Long-running Transactions• Existing businesses do them often• Travel agent scenario

– Multiple resources– Variable cost to change/cancel– Business rules vary – Need some consistent set of tickets/reservations– Need a deterministic agreed outcome

• Compensation rather than rollback (usually)—cancel reservation


Transactions Support Workflow and Choreography

• BPEL4WS• Web Services Choreography Interface (W3C

Note)• ebXML Business Process interactions• Details BTP support for workflows in Potts,

Temel paper (see References)– WSFL– XLANG– BPML


Web Services and Transactions• To integrate transactions and Web services

need to carry one or more of– Correlation ID– Conversation ID (for long-running conversations,

not necessarily transactional—viz. WLStudio)– Transaction context ID (integer, for atomic single-

site)– Additional context information

• Placed in SOAP Header• Potential for conflicts as SOAP Header is used

more and more


Specifications and Standards• When is a specification not a standard?• Is the protocol or API over-specified?

Under-specified?• How interoperable is the protocol?• Automatic or manual configuration?• Optimized for common cases?• Consistent architecture and programming

model?


The Landscape Today

• WS-Transaction + WS-Coordination(WS-T/WS-C)

• OASIS Business Transaction Processing (BTP)

• Others (see references)


WS-Transaction and WS-Coordination• Published August 2002 by BEA, IBM, and

Microsoft• Factors out transaction context management

and propagation into WS-Coordination• XML with Web services binding• Two sub-protocols in WS-T

– Atomic Transactions (AT)– Business Activities (BA)


WS-T and WS-C (continued)

• WS-T/AT (atomic) transactions are essentially traditional and tightly-coupled (ACID) —Atomic, Consistent, Isolated, Durable

• Business Activities are richer and allow for looser coupling, relaxation of Isolation and Atomicity

• Both provide Web service/SOAP bindings


OASIS Business Transaction Protocol• Technical Committee created March 2001 by

BEA, Interwoven, and Sun, soon joined by others

• Committee Specification 1.0 May 2002• XML, with SOAP binding• Two sub-protocols relax ACID properties

– Atoms—Isolation is relaxed – Cohesions—Isolation and Atomicity are relaxed


OASIS BTP(continued)

• Atoms do (mostly) what atomic transactions do• Cohesions do (mostly) what business

processes do, and are similar to WS-T Business Activities

• Most messages are the same across the two protocols (it’s really two kinds of coordinators)


Compare

• Superficial Similarities• Real Similarities• Messages• State Diagrams


Superficial Similarities

• At a high level one might hope that the models align:– WS-T/AT =?= BTP-Atoms– WS-T/BA =?= BTP-Cohesions– WC-Coordination manages contexts as BTP does– Both use XML and Web Services

• But they don’t.• The protocols seem similar• And they are, but optimizations and scalability

are needed for WS-C/WS-T


A Clearer Comparison

XML with SOAP bindingWeb Services

**Atomic TransactionAtoms*

CohesionsBusiness ActivityBTPWS-T/WS-C

• * WS-Transaction doesn’t address this except as a special case of Business Activity

• **BTP doesn’t address this as loosely coupled implementation of tightly-coupled transactions were explicitly ruled out early on


A Clearer Comparison (continued)

• Isolation– WS-T/AT mandates strict isolation, while BTP relaxes

isolation—BTP is more loosely coupled

• Binding– WS-T/WS-C tightly bound to Web Services. BTP is an XML

message protocol with a SOAP binding

• Optimizations– BTP “One Shot” optimization should be used in loosely-

coupled interactions with high latency– BTP allows participants to resign without waiting for

coordinator, and allows timeouts for commitments

• WS-T/AT can work well in a tightly-coupled environment


Real Similarities

• Both WS-T/WS-C and BTP can be used to support business process execution environments, e.g. BPEL4WS, WSFL, WSCI, BPMI, and others

• WS-T Business Activities are similar to BTP Cohesions


Real Similarities (continued)

• Compensating actions are a problem if too common (the protocol should prevent errors and aid recovery)

• Both are useful as an implementingtechnology, e.g. for workflows

• Both are relatively low level and complex• Neither is the only solution in its problem

domain


Real Differences(see references)• WS-T/AT is not loosely-coupled• BTP incorporates optimizations

– One-Shot– Participant resignation– Timeouts

• WS-C/WS-T is under specified—there’s not enough to build interoperable implementations from the specs

• WS-T/AT and WS-T/BA are similar but use different messages

• Factoring out of WS-C complicates the transaction protocol

• BTP is an OASIS Committee Specification


Messages—Normal Case• Normal case: WS-T/AT 1PC or 2PC

• Normal case: WS-T/BA with Completion

• Normal case: BTP

Confirmed || CancelledConfirm || CancelPreparedPrepareRole: InferiorRole: Superior

Closed || CompensatedClose || CompensatePreparedPrepare

Role: ParticipantRole: Coordinator

Committed || AbortedCommit || RollbackPreparedPrepare

Role: ParticipantRole: Coordinator


WS-C/WS-T State Diagram

Ended

Register

Completed ClosingClose

Compensating

Completed Closed

Figure 2: BusinessAgreement Protocol State Diagram

Participant generatedCoordinator generated

Compensated

Cancel

Active

Canceled

Faulted

Faulted Forget

Canceling

Compensate

Exited

Faulted

WS-Transaction Specification BA Figure 2


BTP State Diagram Without Optimizations

Canceling Canceled

Prepare

Prepared Confirmed

Enrolled Completed*

PreparedPreparing Confirming

Auto-Cancel

Auto-Confirm

Enroll/Enrolled

C a n c e lResign/Resigned

(Canceling)

Superior (coordinator) generated Inferior (participant) generated

Confirm

(Confirming)

Contradicted

Cancel

Courtesy Sazi Temel


Ended

Register

Completed ClosingClose

Compensating

Completed Closed

Compensated

Cancel

Active

Canceled

Faulted

Faulted Forget

Canceling

Compensate

Exited

Faulted

WS-T

Canceling Canceled

Prepare

Prepared ConfirmedEnrolled Completed

*PreparedPreparing Confir

ming

Auto-Cancel

Auto-Confirm

Enroll/Enrolled

C a n c e lResign/Resigned

(Canceling)

Superior (coordinator) generated Inferior (participant) generated

Confirm

(Confirming)

Contradicted

Cancel

BTP


Specifications and Standards (again)• When is a specification not a standard?• Is the protocol or API over-specified?

Under-specified?• How interoperable is the protocol?• Automatic or manual configuration?• Optimized for common cases?• Consistent architecture and programming

model?


Driving Convergence

• BTP and WS-Transaction/WS-Coordination overlap in significant areas

• Similar goals, different details• Industry would be well-served by convergence

in this space• Standards submission of WS-Transaction and

WS-Coordination would be the next step in driving convergence


Conclusions

• Both technologies approach broad and complex issues

• Both technologies can support aggregations including composition, workflows, and choreography

• Convergence is going to be important—the industry needs one standard, not two similar-but-different ones

• Either can simplify distributed agreement without making you “roll your own”


References• On BEA, IBM, and Microsoft web sites (only BEA URL listed)

– WS-Transaction • http://dev2dev.bea.com/techtrack/ws-transaction.jsp

– WS-Coordination• http://dev2dev.bea.com/techtrack/ws-coordination.jsp

– BPEL4WS• http://dev2dev.bea.com/techtrack/BPEL4WS.jsp

• OASIS Business Transaction Processing Web site– http://www.oasis-open.org/business-transactions/

http://dev2dev.bea.com/techtrack/ws-transaction.jsp

http://dev2dev.bea.com/techtrack/ws-transaction.jsp

http://dev2dev.bea.com/techtrack/ws-coordination.jsp

http://dev2dev.bea.com/techtrack/BPEL4WS.jsp

http://www.oasis-open.org/business-transactions/

http://www.oasis-open.org/business-transactions/


References (continued)• Choreology Ltd detailed analysis of BTP and WS-

Transaction– Technical discussion

• Link from http://www.choreology.com near bottom left– Peter Furniss and Alastair Green, BTP: WS-T Message

sequence comparisons• http://www.choreology.com/resources/2002-11-

20.message_sequence_comparison.A.ppt

• Papers– Mark Potts & Sazi Temel, Business Transactions in Workflow

and Business Process Management on BTP Web site– Sanjay Dalal, Sazi Temel, Mark Little, Mark Potts, Jim

Webber, Coordinating Business Transactions on the Web, IEEE Internet Computing, Jan/Feb 2003.

• Available on web to IEEE members at http://www.computer.org/internet/ic2003/w1030abs.htm

– Roger Sessions, Shoot-out at the Transaction Corral: BTP versus WS-T at http://www.objectwatch.com/issue_41.htm

http://www.choreology.com/

http://www.choreology.com/

http://www.choreology.com/resources/2002-11-20.message_sequence_comparison.A.ppt

http://www.computer.org/internet/ic2003/w1030abs.htm

http://www.objectwatch.com/issue_41.htm

http://www.objectwatch.com/issue_41.htm


References (continued)

• WSCI– http://www.w3.org/TR/wsci/

• BPML– http://www.bpmi.org/

• XLANG (superseded by BPEL4WS)– http://www.gotdotnet.com/team/xml_wsspecs/xlang-c/

• Web Services Flow Language (superseded by BPEL4WS)– http://www.ibm.com/software/solutions/webservices/pdf/WSFL.pdf

http://www.w3.org/TR/wsci/

http://www.w3.org/TR/wsci/

http://www.bpmi.org/

http://www.gotdotnet.com/team/xml_wsspecs/xlang-c/

http://www.ibm.com/software/solutions/webservices/pdf/WSFL.pdf

http://www.ibm.com/software/solutions/webservices/pdf/WSFL.pdf

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